186250-84-0Relevant academic research and scientific papers
Mechanism of SeO2 promoted oxidative rearrangement of 2-substituted oxazolines to dihydrooxazinones: Isotopic labeling and kinetic studies
Shafer, Cynthia M.,Morse, Daniel I.,Molinski, Tadeusz F.
, p. 14475 - 14486 (1996)
The mechanism of the recently reported SeO2 promoted oxidative rearrangement of 2-alkyl oxazolines was investigated. 13C labeling studies with 1a-2-13C showed that rearrangement proceeds by fission and migration of the C=N bond, not the C-C bond as first proposed. Oxidation-rearrangement of 1 proceeds by rapid SeO2 promoted oxidation to 2-acyloxazoline 3 followed by slower rearrangement of 3 to oxazinone 2. The second order rate constant for the oxidation step for 2,4-diphenyloxazoline 1b in 1,4-dioxane at 40°C was k1 = 2.85 ± 0.62 x 10-2 M-1·s-1. The second and rate limiting rearrangement step (3b → 2b) had a first order rate constant of k2 = 1.15 ± 0.09 x 10-3 s-1 while the relatively low apparent energy of activation E(A) of 4.2 ± 1.6 kcal·mol-1 in the presence of 2.0 equiv of SeO2 suggests heterogeneous catalysis. The reaction is catalyzed by Lewis acids, including SeO2 or small amounts of H2O. A plausible mechanism is proposed involving Lewis acid activation and nucleophilic catalysis with H2O.
